Diamond devotes this whole book to understanding why some societies have come to have wealth and power while others have not. His answer is essentially that geographical luck is what has determined this.

Diamond argues that some places in the world were better places for civilizations to start and to grow. (A good place was one where agriculture could start relatively easily.) This was particularly true of the "continent" of Eurasia. Civilizations started there first and therefore had more time to grow. There were also more civilizations there that could help each other grow.

Because these civilizations were in better places and got started earlier, they became advanced. They were the first to invent agriculture, which eventually allowed them to have "guns, germs, and steel."

So, to Diamond, some societies have so much because they happened to arise in "good" places. It is simply a matter of geographic luck.